Various types of liquid crystal displays (LCD's) have been developed as flat display devices. Among them, those based on active matrix technology are popular. A plurality of source drivers are used in many of the devices because the number of signal lines has increased in order to cope with recent increase in pixel number in pixel matrix sections for high definition.
Use of a plurality of source drivers entails various problems including the following ones: (1) The bonding steps to attach the source drivers increase in number, and productivity falls. (2) Poor yields and defects, such as corrosion caused by a difference in electric potential between terminals, are likely to occur in the source driver bonding steps due to the narrowing of signal line pitches. (3) Boundaries for each source driver develop on the display screen of the display device due to, for example, a difference in characteristics between the source drivers or a difference in contact resistance between terminals.
Patent Literature 1 (see the list below), in order to solve these inconveniences, discloses a display device which eliminates the need to use a plurality of source drivers by providing the display device with a source driver capable of electric signal outputs using one third the terminals of conventional source drivers.
FIG. 21 is a diagram illustrating the entire arrangement of a display device 51 as the display device of Patent Literature 1. As illustrated in FIG. 21, the display device 51 is provided with: a pixel matrix section 55 which includes a matrix of pixels arranged in m rows and n columns; a gate driver 53; and a source driver 52 which outputs a drive signal to each red, green, and blue pixel in the pixel matrix section 55 as time-divided driver output signals. The display device 51 is further provided with a signal distribution device 54 formed monolithically on a TFT substrate. The display device 51 is adapted so that the signal distribution device 54 can distribute the driver output signal outputs from the source driver 52 to the signal lines for the pixel matrix section 55.
FIG. 22 is a diagram illustrating the internal arrangement of the signal distribution device 54. As illustrated in FIG. 22, the signal distribution device 54 includes a matrix of distribution lines 57(1, r), 57(1, g), and 57(1, b) to 57(n, r), 57(n, g), and 57(n, b) which correspond respectively to driver output signals Si_1 to Si_n (n is 2 or a greater integer) which are supplied from the source driver 52 and control lines 59—r, 59—g, and 59—b to which switching signals are applied to switch the distribution lines to which the driver output signals Si_1 to Si_n are fed (r, g, and b denote red, green, and blue respectively).
The distribution lines 57(1, r), 57(1, g), and 57(1, b) to 57(n, r), 57(n, g), and 57(n, b) have their output terminals connected to the signal lines for the pixel matrix section 55. The distribution lines are also connected to respective TFT 60(1, r), 60(1, g), 60(1, b) to 60(n, r), 60(n, g), 60(n, b) as switching elements. The control lines 59—r, 59—g, and 59—b are connected respectively to the gates of the TFT 60(1, r) to 60(n, r), 60(1, g) to 60(n, g), and 60(1, b) to 60(n, b).
FIG. 23 is a timing chart for signals for time-division driving of three distribution lines, for example, the distribution lines 57(1, r), 57(1, g), and 57(1, b), in the display device 51. As illustrated in FIG. 23, first, the source driver 52 outputs a driver output signal Si_k to pixels in the k-th one of the n columns (k is an integer such that 1≦k≦n). At the same time, the driver output signal Si_k is switched by time division according to the switching signals applied to the control lines 59—r, 59—g, and 59—b, so as to be fed to the signal lines for the red, green, and blue pixels in the j-th one of the m rows in the pixel matrix section 55 (j is an integer such that 1≦j≦m).
The red, green, and blue pixels in the j-th row are selected according to a scan signal Vg(j). The scan signals Vg(1) to Vg(m) are applied by the gate driver 53 to the scan lines of the pixel matrix section 55.
The source driver 52, arranged as above, can output electric signals using one third the terminals of conventional source drivers, thereby eliminating the need to provide a plurality of source drivers.
Patent Literature 2 (see the list below) discloses the distribution circuit geometry shown in FIG. 24. The distribution circuit in FIG. 24 has comb-like source and drain electrodes for switching elements 60. The geometry is suited for faster switching speed because it effectively enables wider channel widths.